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Chapter II: Metallurgical Fundamentals
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Chapter II
Metallurgical Fundamentals
Chapter II: Metallurgical Fundamentals
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Content
• Primary Bonds (liên kết)
• Secondary Bonds
• Crystalline Structure
• Theoretical Yield Strength
• Mechanisms of Plastic Deformation
• Strengthening Mechanisms
• Recovery
• Recrystallization
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Chapter II: Metallurgical Fundamentals
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Atomic Bonds
• Primary Bonds: Strong atom-to-atom attractions
by exchange of valence electrons
• Secondary Bonds: Weak attraction between
molecules (van der Waals forces)
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Primary Bonds
• Ionic
• Covalent
• Metallic
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Chapter II: Metallurgical Fundamentals
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Ionic Bonding
Groover (2005)
Ionic Bond (Combination of metallic and nonmetallic elements):
Atoms either get electrons or loose electrons to make their outer shells complete so that
they become positive or negative ions. Opposite charge atoms attract each other.
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Covalent Bonding
Groover (2005)
Covalent Bond (Nonmetallic elements):
Atoms share outer shell electrons.
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Chapter II: Metallurgical Fundamentals
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Metallic Bonding
Groover (2005)
Metallic Bond (Metals and their alloys):
Atoms loose their outer shell electrons and become
“+” ions surrounded by a free electron cloud.
Free electrons act as cement to hold atoms
together.
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Properties of Bonds
Property Ionic Bond Covalent Bond Metallic Bond
Hardness High
Low to
Very High

Low to High
Ductility Brittle Brittle Ductile
Melting Point
Temperature
High
Low to
Very High
Low to High
Electrical &
Thermal
Conductivity
Low Low High


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Chapter II: Metallurgical Fundamentals
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Secondary Bonds
• Dipole forces ['daipoul] Các lực lưỡng cực
• London forces
• Hydrogen bonding
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Dipole Forces
Groover (2005)
Two molecules with dipole
property attract each other
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Chapter II: Metallurgical Fundamentals
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London Forces
Groover (2005)
Two molecules with
temporary dipole property
attract each other
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Hydrogen Bonding
Groover (2005)
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Crystalline Structure
Groover (2005)
Body Centered Cubic
(BCC)
Face Centered Cubic
(FCC)
Hexagonal Closed
Packed (HCP)
Examples
BCC
Chromium (Cr), Iron (Fe), Molybdenum (Mo),
Tantalum (Ta), Tungsten (W)
FCC
Aluminum (Al), Copper (Cu), Gold (Au), Lead
(Pb), Silver (Ag), Nickel (Ni)
HCP
Magnesium (Mg), Titanium (Ti), Zinc (Zn)
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Elastic and Plastic Deformations
undeformed crystal
deformation
elast c i
deformation
elastic and last c p i
undeformed crystal
theoretical
to
30 2
G G
τ
π
=
Elastic deformation of crystal
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Chapter II: Metallurgical Fundamentals
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Theoretical & Actual Strengths
Metal
Shear
Modulus
in MPa
Theoretical
Shear Strength
in MPa
Actual Shear
Strength
in MPa

Steel 75,800 2,527 to 12,063 150 to 750
Aluminum
Alloys
27,500 917 to 4,377 50 to 150
Copper Alloys 41,400 1,380 to 6,589 100 to 250
Titanium Alloys 44,800 1493 to 7,130 350 to 800
Chapter II: Metallurgical Fundamentals
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Plastic deformation of crystal
2 Kinds of plastic deformation:
- Slide/Slip Mechanism
and - Twining Mechanism
Slide/Slip Mechanism
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Chapter II: Metallurgical Fundamentals
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Twining Mechanism
undeformed crystal
deformation
plast c i
t
w
i
n
n
i
n
g

p

l
a
n
e

t
w
i
n
n
i
n
g

p
l
a
n
e

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Imperfections
• Point Defects
– Vacancy
– Ion-Pair Vacancy
– Interstitialcy
– Displaced Ion
• Line Defects
– Edge Dislocation

– Screw Dislocation
• Surface Defects
– Grain Boundaries
Definition:
Imperfections or defects refer to the deviations in the regular
pattern of the crystalline lattice structure.
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Typical Points Defects
vacancy interstitialcy
displaced ion
(Frenkel Defect)
ion-pair vacancy
Groover (2005)
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Animated Point Defects
DMEMS
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Line Defects
• Edge dislocation
• Screw dislocation
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Animated Edge Dislocation
DMEMS
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Animated Screw Dislocation
DMEMS
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Plastic Deformation Mechanism
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Yield Strength of Actual Metals
0
s d p
Y Y Y Y Y
= + ∆ + ∆ + ∆
Y
0
: yield stress in an pure single crystal metal with some dislocations
∆Y
s
: increase in yield strength due to solid solution hardening
∆Y
d
: increase due to dispersion hardening
∆Y
p
: increase due to phase boundaries
Chapter II: Metallurgical Fundamentals
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Values of Strength Components

s i i
i
Y k x
∆ =
∑
For ferritic steel for instance Y
0
is about 30 MPa
Element Si Mn P Ni Mo Cu Sn Al N
k
i
81 18 590 8 15 40 130 24 2300
ICFG Doc. No. 11/01
where x
i
is the weight percentage of the
alloying element and k
i
is a weight factor
y
p
k
Y
d
∆ =
Hall-Petch
relationship
d is the grain size and the constant k
y
ranges between 15 to 24 MPa mm

1/2
for
common steels.
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Effect of Plastic Deformation
Plastic Deformation
T T
< 0.3
m
Yield Stress
Ductility
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Recovery
Heating the deformed metal in a range of 0.3 T
m
< T < 0.5 T
m
will activate diffusion of atoms.
This diffusion of atoms enables the motion of some
dislocations which will cancel each other or restructure
themselves.
Stored energy is relieved.
Residual stresses will be removed, yield stress will reduce
slightly and ductility will increase.
Electrical and thermal properties will be recovered as well.
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Recrystallization
Time
T T > 0.5
m
Primary
Recrystallization
Secondary
Yield Stress
Ductility
Definition:
Temperature at which
the whole structure is
completely
recrystallized within one
hour is named as
recrystallization
temperature
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Dislocations will be re-arranged.
Heat treatment
(a) ch−a ñ (b) ñ ë 525
0
C
(c) ñ ë 550
0
C (d) ñ ë 650
0
C

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Chapter II: Metallurgical Fundamentals
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Mutual Effect of
Temperature and Time
Annealing Temperature
Yield Stress
1
0

h
r
1
0

m
i
n
1

h
r
Annealing Temperature
Yield Stress
High amount of
prior cold work
Moderate amount of
prior cold work
Low amount of
prior cold work

Chapter II: Metallurgical Fundamentals
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Typical Recrystallization Temperatures
Material
Recrystallization
Temperature
Material
Recrystallization
Temperature
C-Steel 550
o
C tin 0 to 40
o
C
Pure-Al 290 to 300
o
C zinc 50 to 100
o
C
Dur-Al 360 to 400
o
C Mo 870
o
C
Cu
200
o
C
(changes drastically with alloying
elements)

W 900-1000
o
C
Lead -50 to 50
o
C Ni 400-600
o
C